JPH067934A - Method for seal-welding end of double tubes - Google Patents

Abstract

PURPOSE:To efficiently execute the formation of an excellent bead by executing a round welding on a primary layer by a TIG method and successively executing build-up welding on and after secondary layer by an MIG method. CONSTITUTION:The tube-end fitting boundary part 4 of the double tubes 3 mechanically fitting two kinds of the metallic tubes of the inside metallic tube 1 and the outside metallic tube 2 is subjected to a round welding on the primary layer by using a welding torch 7 for TIG method and an electrode 8 by the TIG method. Then, the build-up welding succeeding the secondary layer is successively executed to the surface part of the tube by using a welding torch 9 for MIG method and an electrode 10 by the MIG method. The welding electrode for TIG method is arranged at the downward slope by setting the electrode arrangement angle at 20-80 deg., and the welding electrode for MIG method is arranged at the downward slope to execute the welding by setting the electrode arrangement angle at 5-20 deg.. As a filler material, highly alloyed wire is used. By this method, the butting circular welding of the double tubes saving manpower can be executed with high reliability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seal welding method for pipe ends of double pipes used in fields such as oil well pipes for oil and natural gas mining, line pipes for transportation, and pipes for waste liquid treatment plants. It is a thing.

[0002] Pipes exposed to corrosive gases such as hydrogen sulfide and strongly acidic and strongly alkaline waste liquids have high mechanical strength and corrosion resistance, for example, in order to keep production cost within a reasonable range. There is an increasing demand for a double pipe in which a nickel alloy inner metal pipe and a low alloy steel outer metal pipe are mechanically fitted by a shrink fitting method or the like.

[0003]

2. Description of the Related Art Double pipes are formed by joining a series of pipes at a construction site to form a pipeline having a required length. However, the mechanically fitted boundary between the inner metal pipe and the outer metal pipe is small. However, since there is a gap, a blowhole defect may occur due to the gap at the time of butt circumferential welding of pipe ends. Therefore, double pipes are shipped after the pipe ends are pre-sealed at the factory stage and the weld beads are provided with the required groove.

At the time of pipe end seal welding, the TIG (Tig) method in which an arc is generated between a tungsten electrode and a base metal in a shield gas to melt the base metal and the filler metal is used. Since TIG welding has a low deposition rate, it takes a very long time as shown in Table 1 to stack from the inner pipe surface to the outer pipe surface, that is, over the entire thickness of the outer pipe.
Since the welding efficiency for pipe end treatment is poor, the productivity of the entire double pipe is significantly impaired.

[Table 1]

On the other hand, a consumable electrode wire, which also serves as a filler material, is fed at a constant speed, and an arc is generated between the consumable electrode wire and the base material in a shield gas to melt the consumable electrode wire and the base material. ) Method can be expected to have a higher deposition rate than TIG welding, but since the welding input used becomes large and blowhole defects due to gaps frequently occur in the first layer,
Currently, it is not used for pipe end seal welding of double pipes.

[0006]

SUMMARY OF THE INVENTION The present invention was obtained by conducting an analysis from various directions on the welding form at the pipe end fitting boundary and conducting various studies on various welding conditions. The object of the invention is the TIG method and the M
To provide a pipe end seal welding method that effectively utilizes the advantages of both welding methods by specifying the order of application of the IG method, and can effectively suppress formation of blowhole defects and efficiently form good beads. Is.

[0007]

A method of the present invention for performing pipe end seal welding of a double pipe 3 in which two types of metal pipes 1 and 2 are mechanically fitted will be described below with reference to the reference numerals shown in the drawings. The gist is to use the TIG method and the MIG method together and to implement the TIG method prior to the MIG method. That is, the first layer round welding is performed on the pipe end fitting boundary portion 4 of the double pipe 3 by the TIG method, and the laminated welding of the second and subsequent layers is continuously performed by the MIG method up to the pipe surface portion.

In order to satisfactorily form the bead 5 by the first layer welding and each bead 6 by the layered welding of the second layer and thereafter, the welding electrode 8 of the TIG method arranged in the outer space of the tube end of the double tube 3 is formed. The welding electrode 10 of the MIG method is usually arranged at a position on the downhill side, that is, behind the pipe apex P when viewed in the pipe rotation direction R.

The electrode arrangement angle is the angle between the target position of the welding electrode and the pipe vertex P with respect to the pipe center O.
For the G method welding electrode 8, a desirable electrode arrangement angle β is within a range of 20 degrees to 80 degrees. When the electrode arrangement angle β is less than 20 degrees, the welding electrode 8 interferes with the welding electrode 10 of the MIG method, and when it exceeds 80 degrees, the shape of the bead 5 deteriorates.

For the MIG welding electrode 10, the preferred electrode placement angle α is in the range of 5 ° to 20 °. When the electrode arrangement angle α is less than 5 degrees, the beads become mountain-shaped or the molten metal flows backward. If the electrode arrangement angle α exceeds 20 degrees, the molten pool head becomes too large, causing problems such as insufficient melting and forward flow of molten metal.

When performing the first layer welding by the TIG method,
Typically, a high alloy wire 11 is used as a filler material in order to improve the fusion property between the high alloy inner metal tube 1 and the beads 5. Further, when the second layer and subsequent layers are welded by the MIG method, the same kind of high alloy wire is used as the welding electrode 10 in order to improve the fusion property between the bead 5 and the additional bead 6.

From the point of view of high efficiency, it is conceivable to carry out all the laminated welding from the first layer to the final layer by the MIG method, but when the high alloy wire is applied to the first layer welding by the MIG method, As described below, it is difficult to achieve both suppression of blowhole defect generation and good bead formation. Therefore, in the method of the present invention, the first layer welding is performed by the TIG method.

That is, since a high alloy wire (for example, INCO.625) used as a consumable electrode in the MIG method has a remarkably high electric resistance as compared with a low alloy, the amount of juule heat generated at the wire protruding portion is large, Is preheated to high temperature,
As shown in FIG. 6, as compared with the low alloy wire, the wire melting efficiency is higher even with the same welding current, and a large amount of wire is melted even with a small welding input. As a result, the heat input per wire welding amount is reduced, and a bead defect is likely to occur due to insufficient heat. Therefore, in order to obtain a good bead shape, it is necessary to increase the welding input to some extent.

However, as the welding input increases, the amount of molten pool increases, the pool becomes longer, the solidification temperature is about 150 ° C. lower than that of low alloy steel, and the residence time of the molten metal becomes longer. An environment in which the blowholes grow easily is cultivated, and it is difficult to satisfy the requirements of suppressing the generation of blowhole defects and forming good beads at the same time. On the other hand, in TIG welding, since the filler wire and welding input can be controlled independently,
It is suitable for reducing the melt pool to form a good beat without blowhole formation.

[0015]

In the combined welding apparatus of the MIG method and the TIG method shown in FIG. 1, the double pipe 3 horizontally laid down is placed on the pair of left and right turning rolls 12, 12 and rotated in the arrow R direction. The high-alloy wire 11 of the filler material is sequentially fed from the wire feeder 13 to the target position of the welding torch 7 of the TIG method, and the high-alloy wire serving as the filler material and the consumable electrode is supplied to the welding torch 9 of the MIG method. 10 is fed from the wire feeder 14 at a predetermined speed.

The welding torch 9 of the MIG method and the welding torch 7 of the TIG method are set to the required electrode arrangement angles α and β. Next, the welding speed is set, the turning roll 12 is rotated, and at the same time, only the TIG welding is started using the high alloy wire 11, and the pipe end fitting boundary portion 4 is welded only once around the first layer. Then, after the TIG welding is stopped, the turning roll 12
Of the TIG method in which the pipe end fitting boundary portion is sealed and welded, the high alloy wire 10 is used to perform continuous lamination welding to the pipe surface by the MIG method.

After the laminated welding is performed up to the pipe surface as shown in FIG. 5, the bead 5 and the plurality of beads are grooved for butt circumferential welding at the construction site as illustrated by the chain line. It is applied to the assembly of No. 6 and shipped to the construction site as a double pipe with pipe end treatment.

[0018]

EXAMPLE A typical example of a double pipe 3 to which the method of the present invention is applied is one in which a high alloy inner metal pipe 1 and a low alloy steel outer metal pipe 2 are shrink-fitted. Depending on the properties of each end of the outer metal pipe 2 and
A groove for seal welding is applied as shown in FIG.

The electrode arrangement angle α of the welding electrode 10 of the MIG method and the electrode arrangement angle β of the welding electrode 8 of the TIG method are selected within the above range, but both the welding electrode 10 and the welding electrode 8 aim at the pipe surface. It is not limited to the normal line standing at the position, that is, on the straight line passing through the target position of the welding electrode and the pipe center O, and as shown in FIG. 2, the normal line is set within the range of constant receding angles γ and θ. It can also be placed at an angle.

When welding one round to start stacking the next layer, the height of the target position of the welding electrode 10 is increased by the thickness h of the beads 5 and 6 as shown in FIG. The protruding length L of the wire forming 10 is made constant. Also,
Control is performed to move the welding electrode 10 to the groove wall 15 side by an amount corresponding to the groove angle so that the distance x from the groove wall 15 to the tip of the wire becomes constant. By controlling the position of the electrode during the transition of stacking, it is possible to continuously stack and weld the pipe surface portion without interrupting the MIG arc, and avoid the risk of defective penetration.

Made of low alloy steel (API X60) with an outer diameter of 220 mm,
Nine double pipes 3 consisting of an outer metal pipe 2 having a wall thickness of 12 mm and an inner metal pipe 1 made of a high alloy material (ALLOY 825) and having a wall thickness of 2 mm are prepared, and at each pipe end of each double pipe 3. A groove having an angle shown in FIG. 3 was applied. One using only the TIG method (A), one using only the MIG method (B), one using both the TIG method and the MIG method to set the electrode arrangement angle of the MIG method small (C), the TIG method and the MIG As a comparative example, a method (D) in which the electrode arrangement angle of the MIG method is set to a large value by using the above-mentioned method is used as a comparative example, and laminated welding is performed at each pipe end. Further, a combination of the TIG method and the MIG method and variously changing the electrode arrangement angles of the TIG method and the MIG method (E, F, G, H, I) is given as an example of the present invention.
Laminate welding was performed on each tube end. The welding conditions of each comparative example and the present invention example are as shown in Table 2.

[Table 2]

For high alloy wires 10 and 11, INCO.625 (J
IS Z3334 YNiCrMo-3 equivalent) with 1.2 mm diameter was used. Pure argon gas (Ar) is used as the shield gas for the TIG method.
A mixed gas of carbon dioxide gas and argon gas (20% CO ₂ + 80% Ar) was used as the shield gas for the MIG method, and the flow rate of each shield gas was set to 20 1 / min. After welding, the appearance of the beads and the X-ray inspection of the entire circumference of the welded portion were performed after the welding, and the quality of the beads was judged and the presence or absence of pits and blow holes was judged. The results are shown in Table 3.

[Table 3]

In Comparative Example A, the weld bead was good, but
Since the welding time is long, improvement in welding efficiency cannot be expected. In Comparative Example B, the welding efficiency was improved to more than 3 times that of Comparative Example A, but pits were generated in the first layer, and the X-ray inspection showed a blow.
Many hole defects were found. In Comparative Example C, since the electrode arrangement angle of the MIG method was too small, backward flow of the molten metal and the like occurred, resulting in an unstable bead. Comparative example D
However, since the electrode arrangement angle of the MIG method was too large, the molten metal flowed down forward, and an X-ray inspection discovered a fusion failure due to insufficient penetration.

On the other hand, in the invention examples E, F, G, H and I, the beads were all stable and the arc time was 14 to 1 as well.
It is 6 minutes, and the welding efficiency is more than doubled as compared with the conventional method using only the TIG method.

[0025]

As described above, in the pipe end seal welding method for a double pipe according to the present invention, the first layer one-round welding is carried out at the pipe end fitting boundary portion by the TIG method, and the second and subsequent layers are laminated. Since the MIG method is performed continuously up to the pipe surface, the advantages of both welding methods can be effectively exhibited by specifying the application order of the TIG method and the MIG method, so that the occurrence of blowhole defects can be accurately performed. Good bead formation can be performed efficiently while suppressing.

In the method of the present invention, since the TIG method is used only for the first layer welding, the overall reduction in efficiency does not pose a serious problem, and the welding conditions such as the filler material, the electrode arrangement angle, and the welding current are appropriately selected. As a result, the pipe end can be sealed and welded with a welding efficiency more than twice that of the conventional method, and this can greatly improve the productivity of the double pipe with the pipe end treated, and save a considerable cost. It is possible.

As described above, since the pipe end seal welding is perfectly performed, no inspection and repair work of the pipe end groove is required at the construction site, and the double pipe butt circumferential welding is highly reliable. It can be carried out labor-saving and is highly useful in oil mining and construction of transportation facilities.

[Brief description of drawings]

FIG. 1 is a MIG method and TI used for carrying out the method of the present invention.
It is a schematic diagram of the compound welding equipment of G method.

FIG. 2 is a schematic diagram showing a receding angle that each welding electrode of the MIG method and the TIG method can take with respect to the pipe surface.

FIG. 3 is an enlarged view of a pipe end of a double pipe grooved for seal welding.

FIG. 4 is an enlarged view of a pipe end of a double pipe in which laminated welding is performed up to a second layer.

FIG. 5 is an enlarged view of a pipe end of a double pipe in which laminated welding is performed up to a pipe surface portion.

FIG. 6 is a graph showing a relationship between a welding current and a wire deposition amount in the MIG method.

[Explanation of symbols]

 1 inner metal pipe 2 outer metal pipe 3 double pipe 4 pipe end fitting boundary part 5 bead 6 bead 7 TIG welding torch 8 TIG welding electrode 9 MIG welding torch 10 MIG welding electrode 11 high alloy Wire 12 Turning roll 13 Wire feeder 14 Wire feeder 15 Seal welding groove L Wire protrusion length O Pipe center P Pipe apex R Pipe rotation direction h Bead thickness x Distance between groove wall and wire tip α Electrode arrangement angle of MIG method β TIG method electrode arrangement angle

Claims (3)

[Claims] 1. A first-layer one-round welding is performed by a TIG method on a pipe end fitting boundary portion of a double tube in which two kinds of metal tubes are mechanically fitted, and a MIG method is used for a laminated welding of the second and subsequent layers. A pipe end seal welding method for double pipes that is continuously performed up to the pipe surface. 2. TI with an electrode arrangement angle of 20 to 80 degrees
Welding electrode of G method is arranged at the downhill position and the electrode arrangement angle is 5
The pipe end seal welding method according to claim 1, wherein the welding electrode of the MIG method is arranged at a downhill position at an angle of 20 to 20 degrees, and the initial layer welding and the laminated welding of the second and subsequent layers are performed. 3. TI using a high alloy wire as a filler material
The pipe end seal welding method according to claim 1, wherein the first layer welding is performed by the G method, and the second layer and subsequent layers are welded by the MIG method using the same type of high alloy wire.